Carrier interconnection is how separate telecom networks link to each other and agree to exchange traffic. No single carrier reaches every person, building or network, so carriers connect at agreed points and hand traffic across: internet traffic through peering and transit, phone calls through voice interconnects, and Ethernet circuits through network-to-network interfaces (NNIs). Buyers rarely arrange it themselves, but it shapes call quality, internet performance and how off-net circuits are delivered and repaired.
At a glance
- Carriers connect at meet points, typically in carrier hotels, colocation facilities or internet exchanges, or at agreed points between their networks.
- Each traffic type has its own form: IP peering and transit for internet traffic, SIP or legacy trunks for voice, and Ethernet NNIs for data circuits.
- Commercial terms range from settlement-free peering to paid transit, per-minute voice rates and wholesale access charges.
- When your provider uses another carrier’s last mile to reach your site, the circuit crosses an interconnection and two carriers share repair responsibility.
- The quality and diversity of a provider’s interconnections affect your service even when you never see them.
What problem it solves
Every call, packet and circuit that leaves one carrier’s network has to enter another’s. Without interconnection, a customer of one phone company could not call a customer of another, and an internet provider could reach only its own customers. Interconnection is what turns many separate networks into the public phone network and the internet.
For buyers, it also explains how a provider can sell service at addresses where it has no network. The provider buys local access from a carrier that does reach the building and connects it to its own network at an NNI. That expands choice, but it adds a handoff that matters when something goes wrong.
How it works
Physical meet points. Carriers place equipment in shared facilities, such as carrier hotels and carrier-neutral colocation sites, and connect with cross-connects between their cages. Some interconnect at a building or boundary agreed between the two of them. Larger carriers interconnect in several cities for capacity and resilience.
Internet traffic. IP networks exchange routes with Border Gateway Protocol (BGP). In peering, two networks exchange traffic only for their own customers, either directly or across an internet exchange point. In transit, one network pays another to reach the rest of the internet. Where and how well a provider peers affects the latency and reliability you see to particular destinations.
Voice traffic. Phone carriers exchange calls over interconnect trunks, increasingly using SIP over IP rather than older digital circuits. Interconnects carry the information needed to route calls and, in some countries, to verify caller ID, such as the STIR/SHAKEN framework in the United States. Payment for exchanging calls is governed by agreements between carriers and, in many countries, by regulation.
Ethernet and private circuits. Carriers connect their Ethernet networks through external NNIs, which carry many customers’ circuits over one port, each tagged and kept separate. This is how an off-net Ethernet or dedicated internet circuit reaches your building: the local carrier delivers the last mile and hands it to your provider at the NNI. Both carriers must map speeds and classes of service consistently for the circuit to perform as sold.
For placing your own equipment close to carriers and cloud partners, see our Interconnection solution page; for buying internet reach, see IP Transit.
When it matters for buyers
- Circuits at sites outside a provider’s own network. Ask whether each site is on-net or off-net, and who handles repairs on the local carrier’s portion.
- Voice quality and call completion. Persistent problems calling certain carriers or countries often trace to how calls are routed between carriers.
- Internet performance to specific destinations. Slow access to a particular cloud or region can come from where your provider peers and how much capacity it has there.
- Resilience planning. Two providers may reach your site through the same local carrier and the same building entry, which removes the diversity you paid for.
- Choosing a data center or colocation site. Buildings with many carriers present make it easier to connect to the providers and partners you need.
Questions to ask vendors
- Is our address on your own network, or will you use another carrier for the last mile? If so, which one?
- Who owns trouble tickets end to end on an off-net circuit, and what repair times apply to the local carrier’s portion?
- Where do you interconnect with the other carriers and networks our traffic most depends on?
- Do you peer directly with the major cloud and content providers we use, or reach them through transit?
- For voice, how do you route calls to other carriers, and do you pass caller ID attestation where required?
- How are classes of service mapped across the NNI so our traffic keeps its priority?
- If we buy a second circuit from you or another provider, will it use a different local carrier and building entry?
How it differs from an Internet Exchange Point (IXP)
An Internet Exchange Point (IXP) is one venue for one form of carrier interconnection: a shared switching platform where many IP networks peer with each other. Carrier interconnection is the broader practice, covering private peering and transit links, voice interconnects and Ethernet NNIs as well. It also differs from data center interconnect, where an organization links its own data centers and cloud environments, and from enterprise Carrier Ethernet services such as E-Line and Ethernet private lines, which are what customers buy; carrier interconnection is how providers stitch those services together across each other’s networks.